Question: On the first 3 quizzes of her physics class, Stephanie got an average score of 82. What does she need on the next quiz to have an overall average of 84?
Explanation: Let her score on the next quiz be $x$ The sum of all of her scores is then $3 \cdot 82 + x$ The same sum must also be equal to $4 \cdot 84$ Solve: $x = 4 \cdot 84 - 3 \cdot 82 = 90$.